Integrated circuits such as computer chips are manufactured from semiconductor wafers. These wafers are subjected to numerous steps during the process of making integrated circuits. This generally entails transporting a plurality of wafers from one workstation to another for processing by specialized equipment. As part of the processing procedure, wafers may be temporarily stored or shipped in containers to other plants or to end users. Such intra-facility and extra-facility movements may generate or expose the wafers to potential wafer ruining contaminants. In order to reduce the deleterious effect of contaminants on wafers, specialized containers have been developed to minimize the generation of contaminants and to isolate wafers from contaminants exterior to the containers. A principal feature common to these containers is that they are provided with removable doors or closures to enable access to the wafers inside.
Plastic containers have been used for decades for transporting and storing wafers in-between process steps. Such containers have highly controlled tolerances for interfacing with processing equipment as well as the equipment/robots that transport the containers. Moreover, it is desirable in such plastic containers to use components that are attachable and removable without using metallic fasteners such as screws, since metal fasteners can cause particle generation when inserted and removed.
Additional, required or desirable characteristics of containers to transport and/or store semiconductor wafers include light weight, rigidity, cleanliness, limited gaseous emissions, and cost effective manufacturability. The containers provide hermetic or close to hermetic isolation of wafers when the containers are closed. Simply stated, such containers need to keep the wafers clean, uncontaminated, and undamaged. Additionally, carriers need to maintain their capabilities under the rigors of robotic handling which includes lifting the carrier by the robotic flange positioned at the top of the container.
Front opening wafer containers have become the industry standard for transporting and storing large diameter 300 mm wafers. In such, containers the front door is latchable within a door frame of a container portion, and closes a front access opening through which the wafers are robotically inserted and removed. When the container is fully loaded with wafers the door is inserted into the door frame of the container portion and latched thereto. When seated, cushions on the door provide upward, downward, and inward constraint for the wafers.
A seal, generally in the form of a continuous loop of elastomeric material is fastened on the periphery of the door to provide sealing. Typically such seals are attached by inserting a base portion into a groove on the periphery of the door and/or securing the seal on pegs extending through holes in the seal. Often the “loop” of seal material is smaller than the circumference of the groove. This has proved to provide good seal retention on the rounded corners but the tension in the seal does little to retain the seal in the grooves in the large straight expanses of the top, bottom, and sides of the door. Uniformity and consistency of the sealing has been encountered particularly as the openings in wafer containers have increased to accommodate larger wafers.
The semiconductor industry is now moving toward using even larger, 450 mm diameter, wafers. The larger diameter wafers, although providing cost efficiencies, also provide increased fragility, greater weight, and present undiscovered issues associated with handling and storing the larger wafers in containers made of plastic. Deflection and related problems associated with the expanses of plastic on the top, bottom, sides, front, and back are exacerbated, as are door sealing issues due to uneven seals and distortion of the door to door-frame interface due to the deflection of container surfaces.
Along with increasing size of semiconductor wafers, the density of the circuits formed on the wafers has also been increasing, making the circuits more susceptible to defects from smaller and smaller particles and other contaminants. In short, as wafers have increased in size, containers have increased in size as well, and the requirements for keeping the wafers clean and contaminant free have become more stringent due to the wafers being more susceptible to smaller particles and other contaminants.
There are several drawbacks associated with prior wafer handling devices or containers related to particulate generation. During the working life of a container, the closure or door is attached and removed many times by both robotic and manual means. With each attachment and removal, a portion of the door edge may scrape against the door frame of the container. This can result in the generation of loose particles which may become airborne to lodge on the wafers being contained. Equally important, doors of wafer handling devices or containers typically include cushions or channels which contact and support wafer edges. Optimally, such cushions or channels are designed to operate in concert with wafer receiving channels in the containers to securely retain a plurality of wafers. If a door is not, and cannot be accurately and repeatedly centered within a door frame, excessive contact and subsequent particle generation between the door cushions or channels and wafers may occur.
The problem of particle generation may also be attributed to the process by which doors and containers are manufactured. Containers and doors are usually formed by injection molding with plastic such as polycarbonate. Inherent in such molding is shrinkage and warpage of the molded parts. Although plastic injection molding techniques are highly advanced, there still may be individual deviations between different components form the same mold. While slight deviations do not generally compromise the function of a door in closing an container, they can change the working dimensions to the extent that contact (and the resultant particle generation) between a door and a door frame is increased. Dimensional changes can also be generated by the dies themselves, as a result of normal wear and tear. This problem is accentuated when the tolerances of the components of doors and containers are stacked or added.
Yet another drawback occurs because these wafer carriers are robotically opened and closed. The carriers will be opened by multiple pieces of equipment which may each be set up differently. Also such equipment may go out of adjustment and is subject to wear and tear. Such equipment may not then be perfectly aligned resulting in undesirable and/or excessive door-frame contact and a situation of excessive abrasion and/or particle generation.
Accordingly, a need in the industry exists for a wafer container that addresses one or more of these problems, particularly as they exist relative to containers for 450 mm diameter and larger wafers.